This disclosure relates generally to transaction processing, and more particularly to method and system for transaction processing in an application. In one embodiment, the method includes facilitating selection of an overlay application corresponding to the application. The application includes at least one window having a plurality of fields and is rendered in a first UI. At least one field of the plurality of fields is masked to obtain at least one masked field in the first UI. A second UI corresponding to the at least one window is rendered. The second UI is associated with the overlay application and includes at least one field blank field corresponding to the at least one field masked field in the first UI. Entering data is enabled in the at least one blank field in the second UI, and the data entered is compared with a prepopulated data to determine validity of the transaction.